At age 41, he has decided to lay bare almost everything in a tell-all diary called "Bong," a slang term for homosexuals, written by two local journalists after more than 300 hours of taped interviews with him.
Dung is sure many people here won't like his memoir, which has triggered both praise and criticism for its often explicit recollections of sexual adventures and relationships with other men.
But Dung says it was high time to try to change attitudes in Vietnam.
"I don't want to be famous," he told AFP. "Being famous means being notorious, and the price you pay is high. But to achieve my goal, I had to sacrifice my privacy. It wasn't easy. It was a fierce struggle for me."
Very few gay people publicly come out in Vietnam. Homosexuality is still a largely taboo subject in the communist-governed, traditionally patriarchal society, long ruled by Confucian social mores and Buddhist beliefs.
The book had a modest first print run of 2,000 copies. But the fact that it was published at all is considered by many here a sign of changing attitudes and greater tolerance in this fast-changing country.
Many gay men, Dung says in the book, have struggled with deep shame for not meeting societal expectations -- marrying, building a family, taking over the house, caring for their ageing parents and producing male offspring.
"If you were born gay," he writes, "no matter whether you are a man or a woman, you were born at a bad time, on a bad day, in a bad month, in a bad year, under a very bad star."
In one section he speaks of the deep torment he and others have felt.
"If there is the so-called next life, I beg God to let me be an ordinary man or an ordinary woman, whatever gender it may be, but to be as normal as other people. It seems a very simple dream, but for me and my friends being normal is impossible."
The word "bong" can mean shadow or silhouette in Vietnamese and is sometimes used as a moderately derogatory term for homosexual males because it suggests they are mere "shadows of normal men."
Dung, with a tattooed arm and an unusually deep voice, was somewhat of a lady-killer in his 20s, according to friends, but eventually came out three years ago, having spent a lifetime hiding his sexuality.
"I could not pretend to love a woman just to maintain family happiness," he said. "It would have been torture. I cannot live like that. I cannot be another person, rather than myself. I cannot hurt a woman just to cover myself."
He explained in the diary that coming out, or publicly announcing being gay, requires much bravery in Vietnam, saying: "You must be very courageous to rob a beloved son from his parents and to give them back a distorted creature."
Dung started to work with a foreign-funded non-government group in 2005 and last year founded his own self-help gay group called "Green Pine," named after the hardy evergreen tree because it can survive in harsh conditions.
Dung, who used to work in a butcher shop, now devotes much of his time to advocacy work, informing gay and lesbian people about lifestyle and health issues including safe sex, and combating prejudice in the wider society.
"I used to think that I was ill," he writes.
"Only now can I really understand that gays are normal people in terms of health and intellect. We are only different in terms of our sexual tendency."